The spools of a high speed magnetic tape cartridge can rotate at speeds of up to four thousand revolutions per minute. At these rotational speeds any misalignment between the spool and the drive that it is coupled with can result in unacceptable wobbles between the two. Various approaches and mechanisms have been used to compensate for, or eliminate axial misalignment. Since the number of tape cartridges produces exceeds the number of drives by several orders of magnitude, the burden of compensating for axial misalignment has fallen on the drives. A common drive design inserts a complex drive coupling between a fixed axis drive mechanism and the spool. This drive coupling can move parallel to the axis of rotation of the fixed axis drive mechanism, move linearly in any direction in a plane normal to the axis of rotation, and still transfer torque to the spool. When in use, the spool end axis of the drive coupler will orbit the drive mechanism end axis of the drive coupler once or each revolution of the drive mechanism. The greater the axial misalignment between the drive mechanism and the spool, the greater the orbital radius through which the drive coupler must flex. When operated at thousands of revolutions per minute over tens of thousands of hours, the drive couplers are subject to significant wear.
Mechanical tolerances in tape cartridge manufacturing and spool repositioning due to mishandling, such as dropping the cartridges, sometimes cause each spool's axis of rotation to be misaligned with the respective drive mechanism's axis of rotation. Compensation for any such misalignments is usually allocated to the drive coupler. The drive coupler tilts away from the drive mechanism's axis of rotation to align with the spool's axis of rotation. As the drive mechanism rotates through one revolution, the drive coupler tilt precesses through one circle resulting in more wear.
Another desirable feature commonly included in the tape cartridges is a clutch mechanism that locks the spools while the tape cartridge is not in use. The clutch mechanism keeps the tape wound around the spools from spilling off the spools while the tape cartridge is being handled. When the tape cartridge engages the drive coupler, the clutch unlocks to allow the spools to be turned by the drive mechanism. Common designs lock the spools against the housing of the cartridge. Such designs require the cartridges to have sufficient strength and alignment accuracy with respect to the spools to operate as half of the clutch mechanism.